Polyurethane foams for wound management

ABSTRACT

The invention relates to a process for producing polyurethane foams for wound management. These polyurethane wound dressing foams are prepared by a process comprising frothing and drying of a foam foaming composition, which comprises a polyurethane dispersion and specific coagulants.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

The present patent application claims the right of priority under 35 U.S.C. §119 (a)-(d) of German Patent Application No. 10 2006 016 636.1, filed on Apr. 8, 2006.

BACKGROUND OF THE INVENTION

The present invention relates to a process for producing polyurethane wound dressing foams comprising polyurethane wound dressing foams foams which are frothed and dried, in which the polyurethane foams comprise one or more polyurethane dispersions and one or more coagulants.

Polyurethane wound dressing foams are known to be suitable for treating exsudating wounds. Due to their high absorbency and their good mechanical properties, polyurethane foams produced by reaction of mixtures of diisocyanates and polyols or NCO-functional polyurethane prepolymers with water in the presence of certain catalysts and also (foam) additives are generally used. Aromatic diisocyanates are generally employed. Numerous forms of these processes for producing polyurethane foams are known as described in, for example, U.S. Pat. No. 3,978,266, U.S. Pat. No. 3,975,567 and EP 0 059 048. The aforementioned processes, however, have the disadvantage that they require the use of reactive mixtures which contain diisocyanates or corresponding NCO-functional prepolymers, the handling of which is technically inconvenient and costly due to the necessary appropriate protective measures associated with such diisocyanates or NCO-functional prepolymers of these diisocyanates.

One alternative to the above-described process which utilizes diisocyanates or NCO-functional prepolymers, is a process based on polyurethane dispersions (which are essentially free of isocyanate groups) into which air is incorporated by vigorous stirring in the presence of suitable (foam) additives. The so-called mechanical polyurethane foams are obtained after drying and curing. In connection with polyurethane wound dressing foams, such are described in EP 0 235 949 and EP 0 246 723, with the foam either having a self-adherent polymer added to it, or the foam being applied to a film of a self-adherent polymer. In addition, the examples in EP 0 235 949 and EP 0 246 723 require that polyaziridines are used as crosslinkers. Polyaziridines are no longer acceptable, however, because of their toxicity. Moreover, crosslinking requires the use of high baking temperatures, with these temperatures reported to be in the range from 100° C. to 170° C. U.S. Pat. No. 4,655,210 describes the use of the aforementioned mechanical foams for wound dressings which have a specific construction made up of a backing, a foam and a skin contact layer. The foams produced according to the processes described in EP 0 235 949 and EP 0 246 723, moreover, have the immense disadvantage that the foams obtained therein are only minimally open-cell, which reduces the absorbance of physiological saline and also the water or moisture vapor transmission rate.

The management of wounds having a complex topology or the coverage of particularly deep wounds is difficult with ready-to-use, industrially manufactured sheetlike polyurethane wound dressing foams, since optimal covering of the wound surface is generally not accomplished, thus retarding the healing process. To achieve better covering of deep wounds, it has been proposed to use granules of microporous polyurethanes instead of compact wound dressings (see EP-A-0 171 268). However, this also does not achieve optimal covering of the wound.

The application of a (flowable) polyurethane foam forming composition which optimally conforms to the wound shape would eliminate the disadvantages of sheetlike wound dressings. The two processes described above, which utilize either diisocyanates/NCO-functional polyurethane prepolymers or polyurethane dispersions in combination with polyaziridines to produce polyurethane foams, cannot be used for this. Reactive polyurethane foam forming compositions which contain free isocyanate groups cannot be applied directly to the skin, even though this has been variously proposed (see, for example, WO 02/26848). Also, polyurethane dispersions which contain polyaziridines as crosslinkers are not acceptable because this crosslinker has properties which are not generally recognized as safe by toxicologists.

An object of the present invention is to provide polyurethane foams for wound management in which the foam polyurethane foam forming composition is free of isocyanate groups. The production of the polyurethane foam shall in principle also be able to be carried out under ambient conditions, in which case the resultant polyurethane foams, as well as having good mechanical properties, shall have a high absorbence of physiological saline and a high water and moisture vapor transmission rate. This requires that the polyurethane foam have a certain open-cell content. Moreover, the polyurethane foam forming composition shall be suitable for direct application to the skin, for example, by spraying or casting, in order that the wound may be optimally covered with the polyurethane foam, which makes rapid drying essential for this polyurethane foam forming composition.

SUMMARY OF THE INVENTION

It has now been found that polyurethane foam forming compositions containing polyurethane dispersions and specific cationic coagulants, both free of isocyanate groups, can be used to produce at ambient conditions polyurethane foams having good mechanical properties, a high absorbence of physiological saline and a high water and moisture vapour transmission rate. The polyurethane foams exhibit, at least to some extent, an open-cell pore structure. The flowable polyurethane foam forming compositions, moreover, can be applied directly to the skin by spraying or casting.

The present invention accordingly provides a process for producing polyurethane wound dressing foams made of a frothed and dried polyurethane foam which comprises (I) at least one aqueous, anionically hydrophilicized polyurethane dispersion and (II) at least one cationic coagulant.

For purposes of the present invention, polyurethane wound dressing foams are porous materials, preferably having at least some open-cell content, which are made of polyurethanes. These materials protect wounds against germs and environmental influences like a sterile covering, and they have a fast and high absorbence of physiological saline (i.e. more precisely wound fluid), a suitable permeability for moisture to ensure a suitable wound climate, and sufficient mechanical strength.

Suitable aqueous, anionically hydrophilicized polyurethane dispersions to be used as component (I) in the polyurethane foam forming compositions essential to the present invention comprise the reaction product of:

-   -   A) one or more isocyanate-functional prepolymers which comprise         the reaction product of:         -   A1) at least one organic polyisocyanate,         -   with         -   A2) at least one polymeric polyol having a number average             molecular weight in the range from 400 to 8000 g/mol,             preferably in the range from 400 to 6000 g/mol and more             preferably in the range from 600 to 3000 g/mol, and an OH             functionality in the range from 1.5 to 6, preferably in the             range from 1.8 to 3, more preferably in the range from 1.9             to 2.1,         -   and         -   A3) optionally, one or more hydroxyl-functional compounds             having molecular weights in the range from 62 to 399 g/mol,         -   and         -   A4) optionally, one or more isocyanate-reactive, anionic or             potentially anionic and/or optionally nonionic             hydrophilicizing agents;     -   with     -   B) one or more compounds selected from the group consisting of:         -   B1) optionally, one or more amino-functional compounds             having molecular weights in the range from 32 to 400 g/mol,         -   and         -   B2) one or more isocyanate-reactive, preferably             amino-functional, anionic or potentially anionic             hydrophilicizing agents,

in which the free NCO groups of A) said prepolymers are wholly or partially reacted with isocyanate-reactive groups of B) by chain extension, and in which the prepolymers are dispersed in water before, during or after the reaction with component B), and with any potential ionic groups present being converted into the ionic form by partial or complete reaction with a neutralizing agent.

To achieve anionic hydrophilicization, components A4) and/or B2) contain hydrophilicizing agents that have at least one NCO-reactive group such as amino, hydroxyl and/or thiol groups, and additionally have —COO⁻ or —SO₃ ⁻ or —PO₃ ²⁻ as anionic groups or their wholly or partly protonated acid forms as potential anionic groups.

DETAILED DESCRIPTION OF THE INVENTION

The preferred aqueous, anionic polyurethane dispersions used as component (I) have a low degree of hydrophilic anionic groups. More specifically, these preferably have from 0.1 to 15 milliequivalents of hydrophilic anionic groups per 100 g of solid resin (i.e. solid polyurethane).

To achieve good sedimentation stability, the number average particle size of the specific polyurethane dispersions is preferably less than 750 nm and more preferably less than 500 nm. As used herein, the number average particle size is determined by laser correlation spectroscopy.

In the production of A) the isocyanate-functional prepolymer from components A1) to A4), the molar ratio of components which contain isocyanate groups to components which contain isocyanate-reactive groups is in the range from 1.05 to 3.5, preferably from 1.2 to 3.0 and more preferably in the range from 1.3 to 2.5, for the preparation of the NCO-functional prepolymers used as component A).

The amino-functional compounds used as components B1) and B2) are present in such an amount that the equivalent ratio of isocyanate-reactive amino groups of these compounds in component B) to the free isocyanate groups of the prepolymer A) is in the range from 40 to 150%, preferably between 50 and 125% and more preferably between 60 and 120%.

Suitable polyisocyanates to be used as component A1) include the well-known aromatic, araliphatic, aliphatic and/or cycloaliphatic polyisocyanates which have an NCO functionality of ≧2.

Some examples of such suitable polyisocyanates are 1,4-butylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 2,2,4- and/or 2,4,4-trimethylhexamethylene diisocyanate, the isomeric bis(4,4′-isocyanatocyclohexyl)methanes or their mixtures of any desired isomer content, 1,4-cyclohexylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluene diisocyanate, 1,5-naphthalene diisocyanate, 2,2′- and/or 2,4′- and/or 4,4′-diphenylmethane diisocyanate, 1,3- and/or 1,4-bis-(2-isocyanatoprop-2-yl)benzene (TMXDI), 1,3-bis(isocyanatomethyl)benzene (XDI), and also alkyl 2,6-diisocyanatohexanoates (i.e. lysine diisocyanates) having C₁-C₈-alkyl groups.

In addition to the aforementioned polyisocyanates, it is also possible to use, proportionally, modified diisocyanates of uretdione, isocyanurate, urethane, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structure and also non-modified polyisocyanate having more than 2 NCO groups per molecule such as, for example, 4-isocyanatomethyl-1,8-octane diisocyanate (i.e. nonane triisocyanate) or triphenylmethane 4,4′,4″-triisocyanate.

Preferably, the polyisocyanates or polyisocyanate mixtures of the aforementioned kind have exclusively aliphatically and/or cycloaliphatically attached isocyanate groups and an average NCO functionality in the range from 2 to 4, more preferably in the range from 2 to 2.6 and most preferably in the range from 2 to 2.4 for the mixture.

It is particularly preferred for component A1) to comprise 1,6-hexamethylene diisocyanate, isophorone diisocyanate, the isomeric bis(4,4′-isocyanatocyclo-hexyl)methanes or also mixtures thereof.

Component A2) comprises at least one polymeric polyol having a number average molecular weight M_(n) in the range from 400 to 8000 g/mol, preferably from 400 to 6000 g/mol and more preferably from 600 to 3000 g/mol. These polymeric polyols preferably have an OH functionality in the range from 1.5 to 6, more preferably from 1.8 to 3 and most preferably from 1.9 to 2.1.

Such polymeric polyols are the well-known polyester polyols, polyacrylate polyols, polyurethane polyols, polycarbonate polyols, polyether polyols, polyester polyacrylate polyols, polyurethane polyacrylate polyols, polyurethane polyester polyols, polyurethane polyether polyols, polyurethane polycarbonate polyols and polyester polycarbonate polyols which are commonly used in polyurethane coating technology. These can be used either individually or in any desired mixtures with one another as component A2).

These polyester polyols are the well-known polycondensates formed from di- and also optionally tri- and tetraols with di- and also optionally tri- and tetracarboxylic acids or hydroxy carboxylic acids or lactones. Instead of the free polycarboxylic acids, it is also possible to use the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols for preparing the polyesters.

Examples of suitable diols are ethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycols such as polyethylene glycol, as well as 1,2-propanediol, 1,3-propanediol, butanediol(1,3), butanediol(1,4), hexanediol(1,6) and isomers thereof, neopentyl glycol or neopentyl glycol hydroxypivalate. Preferred diols include hexanediol(1,6) and isomers thereof, neopentyl glycol and neopentyl glycol hydroxypivalate. In addition to these, it is also possible to use polyols such as trimethylolpropane, glycerol, erythritol, pentaerythritol, trimethylolbenzene or trishydroxyethyl isocyanurate.

Suitable dicarboxylic acids include, for example, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, glutaric acid, tetrachlorophthalic acid, maleic acid, fumaric acid, itaconic acid, malonic acid, suberic acid, 2-methylsuccinic acid, 3,3-diethyl glutaric acid and/or 2,2-dimethylsuccinic acid. The corresponding anhydrides can also be used as a source of an acid.

When the average functionality of the polyol to be esterified is greater than 2, monocarboxylic acids, such as benzoic acid and hexanecarboxylic acid, can be used as well.

Preferred carboxylic acids are aliphatic or aromatic acids of the aforementioned kind. Adipic acid, isophthalic acid and optionally trimellitic acid are particularly preferred.

Hydroxy carboxylic acids which are useful reactants in the preparation of a polyester polyol having terminal hydroxyl groups include, for example, hydroxycaproic acid, hydroxybutyric acid, hydroxydecanoic acid, hydroxystearic acid and the like. Suitable lactones include, for example, caprolactone, butyrolactone and homologues. Caprolactone is preferred.

Likewise, component A2) may comprise at least one hydroxyl-containing polycarbonate, preferably at least one polycarbonate diol, which have a number average molecular weight M_(n) in the range from 400 to 8000 g/mol and preferably in the range from 600 to 3000 g/mol. These are obtainable by the reaction of carbonic acid derivatives, such as diphenyl carbonate, dimethyl carbonate or phosgene, with polyols, preferably diols.

Examples of such diols are ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4-bishydroxymethylcyclohexane, 2-methyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, dipropylene glycol, polypropylene glycols, dibutylene glycol, polybutylene glycols, bisphenol A and lactone-modified diols of the aforementioned kind.

The polycarbonate diol preferably contains 40% to 100% by weight of hexanediol, with preference being given to 1,6-hexanediol and/or hexanediol derivatives. Such hexanediol derivatives are based on hexanediol and have ester or ether groups as well as terminal OH groups. Such derivatives are obtainable by the reaction of hexanediol with excess caprolactone, or by etherification of hexanediol with itself to form di- or trihexylene glycol.

In lieu of or in addition to pure polycarbonate diols, polyether-polycarbonate diols are also suitable for use as A2) a polymeric polyol.

Hydroxyl-containing polycarbonates preferably have a linear construction.

Component A2) may likewise comprise at least one polyether polyols.

Suitable polyether polyols include, for example, the well-known polytetramethylene glycol polyethers which are obtainable by polymerization of tetrahydrofuran by means of cationic ring opening. Such polyether polyols are known and described in various texts dealing with polyurethane chemistry.

Suitable polyether polyols likewise include the well-known addition products of styrene oxide, ethylene oxide, propylene oxide, butylene oxides and/or epichlorohydrin onto di- or polyfunctional starter molecules. The polyether polyols based on the at least proportional addition of ethylene oxide onto di- or polyfunctional starter molecules can also be used as component A4) (i.e. nonionic hydrophilicizing agents).

Suitable starter molecules for the preparation of polyether polyols include all known hydroxyl-group and/or amine-group containing compounds such as, for example, water, butyl diglycol, glycerol, diethylene glycol, trimethylolpropane, propylene glycol, sorbitol, ethylenediamine, triethanolamine, 1,4-butanediol. These starter molecules contain at least one (and preferably more than one) isocyanate-reactive group. Preferred starter molecules are water, ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol and butyl diglycol.

In a particularly preferred embodiment of (I) the polyurethane dispersions, component A2) comprises a mixture of at least one polycarbonate polyol and at least one polytetramethylene glycol polyol, with the proportion of polycarbonate polyols in this mixture being in the range from 20% to 80% by weight and the proportion of polytetramethylene glycol polyols in this mixture being in the range from 80% to 20% by weight, with the sum of the %'s by weight for the polycarbonate polyols and polytetramethylene glycol polyols totals 100%. Preference is given to a proportion of 30% to 75% by weight for polytetramethylene glycol polyols and to a proportion of 25% to 70% by weight for polycarbonate polyols. Particular preference is given to a proportion of 35% to 70% by weight for polytetramethylene glycol polyols and to a proportion of 30% to 65% by weight for polycarbonate polyols. In addition, the proportion of component A2) which is accounted for by the sum total of the polycarbonate and polytetramethylene glycol polyether polyols is at least 50% by weight, preferably 60% by weight, and more preferably at least 70% by weight, based on 100% by weight of A2).

Suitable compounds to be used as component A3) have molecular weights of 62 to 400 g/mol.

Component A3) may utilize polyols of the specified molecular weight range which contain up to 20 carbon atoms, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,3-butylene glycol, cyclohexanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, neopentyl glycol, hydroquinone dihydroxyethyl ether, bisphenol A (2,2-bis(4-hydroxyphenyl)-propane), hydrogenated bisphenol A, (2,2-bis(4-hydroxycyclohexyl)propane), trimethylolpropane, glycerol, pentaerythritol and also any desired mixtures thereof with one another.

Also suitable are ester diols of the specified molecular weight range such as, for example, α-hydroxybutyl-ε-hydroxycaproic acid ester, ω-hydroxyhexyl-γ-hydroxybutyric acid ester, β-hydroxyethyl adipate or bis(β-hydroxyethyl) terephthalate.

Component A3) may additionally comprise monofunctional isocyanate-reactive hydroxyl-containing compounds. Examples of such monofunctional compounds are ethanol, n-butanol, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, 2-ethylhexanol, 1-octanol, 1-dodecanol, 1-hexadecanol, etc.

Preferred compounds to be used as component A3) are 1,6-hexanediol, 1,4-butanediol, neopentyl glycol and trimethylolpropane.

Component A4) herein which is also optional, comprises one or more isocyanate-reactive, anionic or potentially anionic and optionally nonionic hydrophilicizing agents. Thus, the suitable isocyanate-reactive hydrophilicizing agents herein additionally contain one or more of anionic groups, potentially anionic groups and/or nonionic groups.

Suitable anionically or potentially anionically hydrophilicizing compounds to be used as component A4) are any compounds which have at least one isocyanate-reactive group such as a hydroxyl group and also at least one other type of functionality, i.e. a functionality that is not an isocyanate-reactive group. Such functionalities include for example —COO⁻M⁺, —SO₃ ⁻M⁺, and/or —PO(O⁻M⁺)₂ in which M⁺ represents, for example, a metal cation, H⁺, NH₄ ⁺, NHR₃ ⁺, in which each R independently represents a C₁-C₁₂-alkyl group, a C₅-C₆-cycloalkyl group or a C₂-C₄-hydroxyalkyl group. This functionality enters a pH-dependent dissociative equilbrium on interaction with aqueous media, and can thereby have a negative or neutral charge. Some useful anionically or potentially anionically hydrophilicizing compounds include, for example, mono- and dihydroxy carboxylic acids, mono- and dihydroxy sulfonic acids and also mono- and dihydroxy phosphonic acids and their salts. Specific examples of such anionic or potentially anionic hydrophilicizing agents are dimethylolpropionic acid, dimethylolbutyric acid, hydroxypivalic acid, malic acid, citric acid, glycolic acid, lactic acid and the propoxylated adduct formed from 2-butenediol and NaHSO₃ and which is described in, for example, U.S. Pat. No. 4,108,814 (which is believed to correspond to DE-A 2 446 440, see page 5-9, formula I-III therein), the disclosure of which is hereby incorporated by reference. Preferred anionic or potentially anionic hydrophilicizing agents for component A4) are those of the aforementioned kind that have carboxylate or carboxyl groups and/or sulfonate groups.

Particularly preferred anionic or potentially anionic hydrophilicizing agents are those that contain carboxylate or carboxyl groups as ionic or potentially ionic groups, such as dimethylolpropionic acid, dimethylolbutyric acid and hydroxypivalic acid and salts thereof.

Useful nonionically hydrophilicizing compounds which are suitable for use as component A4) include, for example, polyoxyalkylene ethers which contain at least one hydroxyl or amino group, and preferably at least one hydroxyl group.

Examples of these are the monohydroxyl-functional polyalkylene oxide polyether alcohols which contain on average 5 to 70 and preferably 7 to 55 ethylene oxide units per molecule, and are obtainable in a conventional manner by alkoxylation of suitable starter molecules. Such a process is described in, for example, Ullmanns Encyclopädie der technischen Chemie, 4th edition, volume 19, Verlag Chemie, Weinheim pages 31-38.

Obviously such compounds can not be simultaneously be used as component A2) and A4). Thus, if component A2) comprises a polyether polyol prepared by addition of ethylene oxide onto suitable starter molecules, then component A4) is another type of hydrophilicizing agent. Similarly, if component A4) comprises a polyethylene oxide ether then component A2) is another type of polymeric polyol. In this manner, components A2) and a4) are mutually exclusive.

These compounds are either pure polyethylene oxide ethers or mixed polyalkylene oxide ethers, containing at least 30 mol % and preferably at least 40 mol % of ethylene oxide units, based on all alkylene oxide units present.

Preferred polyethylene oxide ethers of the aforementioned kind are monofunctional mixed polyalkylene oxide polyethers having 40 to 100 mol % of ethylene oxide units and 0 to 60 mol % of propylene oxide units.

Preferred nonionically hydrophilicizing compounds for component A4) include those of the aforementioned kind that are block (co)polymers prepared by blockwise addition of alkylene oxides onto suitable starters.

Suitable starter molecules for such nonionic hydrophilicizing agents include saturated monoalcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, the isomeric pentanols, hexanols, octanols and nonanols, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, cyclohexanol, the isomeric methylcyclohexanols or hydroxymethylcyclohexane, 3-ethyl-3-hydroxymethyloxetane or tetrahydrofurfuryl alcohol, diethylene glycol monoalkyl ethers such as, for example diethylene glycol monobutyl ether, unsaturated alcohols such as allyl alcohol, 1,1-dimethylallyl alcohol or oleic alcohol, aromatic alcohols such as phenol, the isomeric cresols or methoxy-phenols, araliphatic alcohols such as benzyl alcohol, anis alcohol or cinnamyl alcohol, secondary monoamines such as dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, bis(2-ethylhexyl)amine, N-methylcyclohexylamine, N-ethylcyclohexylamine or dicyclohexylamine and also heterocyclic secondary amines such as morpholine, pyrrolidine, piperidine or 1H pyrazole. Preferred starter molecules are saturated monoalcohols of the aforementioned kind. Particular preference is given to using diethylene glycol monobutyl ether or n-butanol as starter molecules.

The useful alkylene oxides for the alkoxylation reaction are, in particular, ethylene oxide and propylene oxide, which can be used in any desired order or else in admixture in the alkoxylation reaction.

Suitable compounds to be used as component B1) in accordance with the present invention include di- or polyamines such as 1,2-ethylenediamine, 1,2-diamino-propane, 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, isophoronediamine, isomeric mixtures of 2,2,4- and 2,4,4-trimethyl-hexamethylenediamine, 2-methylpentamethylenediamine, diethylenetriamine, triaminononane, 1,3-xylylenediamine, 1,4-xylylenediamine, α,α,α′,α′-tetramethyl-1,3- and -1,4-xylylenediamine and 4,4-diaminodicyclohexylmethane and/or dimethylethylenediamine. It is also possible but less preferable to use hydrazine or also hydrazides such as adipohydrazide.

Component B1) can also include compounds which, in addition to a primary amino group, also have one or more secondary amino groups or which also have one or more OH groups in additional to an amino group (either primary or secondary). Examples thereof are primary/secondary amines, such as diethanol-amine, 3-amino-1-methylaminopropane, 3-amino-1-ethylaminopropane, 3-amino-1-cyclohexylaminopropane, 3-amino-1-methylaminobutane, alkanolamines such as N-aminoethylethanolamine, ethanolamine, 3-aminopropanol, neopentanol-amine, etc.

In addition, component B1) can comprise monofunctional isocyanate-reactive amine compounds, for example, methylamine, ethylamine, propylamine, butylamine, octylamine, laurylamine, stearylamine, isononyloxypropylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, N-methylaminopropylamine, diethyl(methyl)aminopropylamine, morpholine, piperidine, or suitable substituted derivatives thereof, amide-amines formed from diprimary amines and monocarboxylic acids, monoketimes of diprimary amines, primary/tertiary amines, such as N,N-dimethylaminopropylamine.

Preferred compounds for component B1) are 1,2-ethylenediamine, 1,4-diaminobutane and isophoronediamine.

Suitable anionically or potentially anionically hydrophilicizing compound to be used as component B2) include any compound which has at least one isocyanate-reactive group, preferably an amino group, and also at least one type of functionality (i.e. a functionality that is not an isocyanate-reactive group) such as, for example, —COO⁻M⁺, —SO₃ ⁻M⁺, —PO(O⁻M⁺)₂ in which M⁺ represents, for example, a metal cation, H⁺, NH₄ ⁺, or NHR₃ ⁺, in which each R independently represents a C₁-C₁₂-alkyl group, a C₅-C₆-cycloalkyl group or a C₂-C₄-hydroxyalkyl group. This functionality enters a pH dependent dissociative equilibrium upon interaction with aqueous media, and can thereby can have a negative or neutral charge.

Some suitable anionically or potentially anionically hydrophilicizing compounds for the present invention are mono- and diamino carboxylic acids, mono- and diamino sulfonic acids and also mono- and diamino phosphonic acids and their salts. Examples of such anionic or potentially anionic hydrophilicizing agents are N-(2-aminoethyl)-β-alanine, 2-(2-aminoethylamino)ethanesulfonic acid, ethylenediaminepropylsulfonic acid, ethylenediaminebutylsulfonic acid, 1,2- or 1,3-propylenediamine-β-ethylsulfonic acid, glycine, alanine, taurine, lysine, 3,5-diaminobenzoic acid and the addition product of IPDA and acrylic acid. Such addition products of IPDA and acrylic acid are described in, for example, EP-A 0 916 647 (Example 1) which is believed to correspond to CA 2,253,119, the disclosures of which are hereby incorporated by reference. It is also possible to use cyclohexylaminopropanesulfonic acid (CAPS) as described in WO-A 01/88006 which is believed to correspond to U.S. Pat. No. 6,767,958, the disclosure of which is hereby incorporated by reference, as anionic or potentially anionic hydrophilicizing agent.

Preferred anionic or potentially anionic hydrophilicizing agents for component B2) are those of the aforementioned kind that have carboxylate or carboxyl groups and/or sulfonate groups, such as the salts of N-(2-aminoethyl)-β-alanine, of 2-(2-aminoethylamino)ethanesulfonic acid or of the addition product of IPDA and acrylic acid (see Example 1 of EP-A 0 916 647).

Mixtures of anionic or potentially anionic hydrophilicizing agents and nonionic hydrophilicizing agents can also be used.

A preferred embodiment for producing the specific polyurethane dispersions comprises components A1) to A4) and B1) to B2) in the following amounts, with the sum of the individual amounts always adding up to 100% by weight:

5% to 40% by weight of component A1),

55% to 90% by weight of component A2),

0.5% to 20% by weight of the sum total of components A3) and B1), and

0.1 % to 25% by weight of the sum total of the components A4) and B2), wherein from 0.1% to 5% by weight of anionic or potentially anionic hydrophilicizing agents from components A4) and/or B2) are present, based on 100% by weight of components A1) to A4) and B1) to B2).

A particularly preferred embodiment for producing the specific polyurethane dispersions comprises components A1) to A4) and B1) to B2) in the following amounts, with the sum of the individual amounts always adding up to 100% by weight:

5% to 35% by weight of component A1),

60% to 90% by weight of A2),

0.5% to 15% by weight of the sum total of components A3) and B1), and

0.1% to 15% by weight of the sum total of the components A4) and B2), wherein from 0.2% to 4% by weight of anionic or potentially anionic hydrophilicizing agents from components A4) and/or B2) are present, based on 100% by weight of components A1) to A4) and B1) to B2).

A very particularly preferred embodiment for producing the specific polyurethane dispersions comprises components A1) to A4) and B1) to B2) in the following amounts, with the sum of the individual amounts always adding up to 100% by weight:

10% to 30% by weight of component A1),

65% to 85% by weight of A2),

0.5% to 14% by weight of the sum total of components A3) and B1), and

0.1% to 13.5% by weight of the sum total of the components A4) and B2), wherein from 0.5% to 3.0% by weight of anionic or potentially anionic hydrophilicizing agents from components A4) and/or B2) are present, based on 100% by weight of components A1) to A4) and B1) to B2).

The production of (I) the anionically hydrophilicized polyurethane dispersions (I) can be carried out in one or more stages in homogeneous phase or, in the case of a multistage reaction, partly in disperse phase. After completely or partially conducted polyaddition of components A1) to A4), a dispersing, emulsifying or dissolving step is carried out. This is followed, if appropriate, by a further polyaddition or modification in the disperse phase.

Any of the known prior art processes can be used. Specific examples of such processes being the prepolymer mixing process, the acetone process or the melt dispersing process. The acetone process is preferred.

Production by the acetone process typically involves the constituents A2) to A4) and the polyisocyanate component A1) being wholly or partly introduced as an initial charge to produce an isocyanate-functional polyurethane prepolymer, and optionally diluted with a water-miscible but isocyanate-inert solvent and heated to temperatures in the range from 50 to 120° C. The rate of the isocyanate addition reaction can be increased using the catalysts known in polyurethane chemistry.

Useful solvents include the customary aliphatic, keto-functional solvents such as acetone, 2-butanone, etc., which can be added not just at the start of the production process but also later, and optionally in portions. Acetone and 2-butanone are preferred.

Other solvents such as xylene, toluene, cyclohexane, butyl acetate, methoxypropyl acetate, N-methylpyrrolidone, N-ethylpyrrolidone, solvents having ether or ester units can additionally be used or wholly or partly distilled off, or in the case of N-methylpyrrolidone and/or N-ethylpyrrolidone, remain completely in the dispersion. Preference is however given to not using any other solvents apart from the customary aliphatic, keto-functional solvents.

Subsequently, any constituents of A1) to A4) not added at the start of the reaction are added.

In the production of the A) the isocyanate-functional prepolymer from components A1) to A4), the molar ratio of components which contain isocyanate groups to components which contain isocyanate-reactive groups is in the range from 1.05 to 3.5, preferably in the range from 1.2 to 3.0 and more preferably in the range from 1.3 to 2.5.

The reaction of components A1) to A4) to form A) the prepolymer is effected partially or completely, but preferably completely. Isocyanate-functional prepolymers which contain free isocyanate groups are obtained in this way, without a solvent or in solution.

The neutralizing step to effect either partial or complete conversion of potentially anionic groups into anionic groups utilizes bases such as tertiary amines such as, for example, trialkylamines having 1 to 12 and preferably 1 to 6 carbon atoms and more preferably 2 to 3 carbon atoms in every alkyl radical or alkali metal bases such as the corresponding hydroxides.

Examples thereof are trimethylamine, triethylamine, methyldiethylamine, tripropylamine, N-methylmorpholine, methyldiisopropylamine, ethyldiisopropylamine and diisopropylethylamine. The alkyl radicals may also contain, for example, hydroxyl groups, such as in the case of the dialkylmonoalkanol-, alkyldialkanol- and trialkanolamines. Useful neutralizing agents further include if appropriate inorganic bases, such as aqueous ammonia solution, sodium hydroxide or potassium hydroxide.

Preference is given to bases such as ammonia, triethylamine, triethanolamine, dimethylethanolamine or diisopropylethylamine, and also sodium hydroxide and potassium hydroxide. It is particularly preferred that the base be selected from the group consisting of sodium hydroxide and potassium hydroxide.

The bases are employed in an amount which is between 50 and 125 mol %, and preferably between 70 and 100 mol %, based on the quantity of substance containing the acid groups to be neutralized. Neutralization can also be effected at the same time as the dispersing step, by including the neutralizing agent in the water of dispersion.

Subsequently, in a further process step, if this has not already been done or has only partially been done, the resultant prepolymer is dissolved with the aid of aliphatic ketones such as acetone or 2-butanone.

In the chain extension of the isocyanate-functional prepolymers A) with component B), the NH₂— and/or NH-functional components are reacted by chain extension, either partially or completely, with the remaining isocyanate groups of the prepolymer. Preferably, the chain extension/termination is carried out before dispersion of the prepolymers in water.

Chain termination is typically carried out using component B1) one or more amines having an isocyanate-reactive group such as methylamine, ethylamine, propylamine, butylamine, octylamine, laurylamine, stearylamine, isononyloxypropylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, N-methylaminopropylamine, diethyl(methyl)aminopropylamine, morpholine, piperidine or suitable substituted derivatives thereof, amide-amines formed from diprimary amines and monocarboxylic acids, monoketimes of diprimary amines, primary/tertiary amines, such as N,N-dimethylaminopropylamine.

When partial or complete chain extension is carried out using component B2) one or more anionic or potentially anionic hydrophilicizing agents as described hereinabove with NH₂ or NH groups, it is preferred that chain extension of A) the isocyanate-functional prepolymers is carried out before dispersion of the prepolymers in water.

The aminic components B1) and B2) can optionally be used in water- or solvent-diluted form in the process of the present invention. These components may be used either individually or in mixtures, with any order of addition being possible in principle.

When water or organic solvent is used as a diluent, the diluent content of component B) is preferably in the range from 70% to 95% by weight, based on 100% by weight of component B).

Dispersion of the prepolymer is preferably carried out following chain extension. For dispersion, the dissolved and chain-extended polyurethane polymer is either introduced into the dispersing water, if appropriate by substantial shearing, such as vigorous stirring for example, or conversely the dispersing water is stirred into the chain-extended polyurethane polymer solutions. It is preferable to add the water to the dissolved chain-extended polyurethane polymer.

Any solvent that is still present in the dispersions after the dispersing step is then typically removed by distillation. Removal during the dispersing step is likewise possible.

The residual level of organic solvents in (I) the polyurethane dispersions is typically less than 1.0% by weight and preferably less than 0.5% by weight, based on 100% by weight of the dispersion.

The pH of (I) the polyurethane dispersions which are essential to the present invention is typically less than 9.0, preferably less than 8.5, more preferably less than 8.0 and most preferably is in the range from 6.0 to 7.5.

The solids content of (I) the polyurethane dispersions is preferably in the range from 40% to 70%, more preferably in the range from 50% to 65%, most preferably in the range from 55% to 65% and especially preferably from 60% to 65% by weight (based on 100% by weight of the dispersions).

Component (II) of the polyurethane foam forming compositions herein comprise at least one coagulant. Suitable coagulants can be any organic compound which contains at least 2 cationic groups, preferably any known cationic flocculating and/or precipitating agent of the prior art. Such coagulants include, for example, a cationic homo- or copolymer of a salt of poly[2-(N,N,N-trimethylamino)ethyl acrylate], of polyethyleneimine, of poly[N-(dimethylaminomethyl)acrylamide], of a substituted acrylamide, of a substituted methacrylamide, of N-vinylformamide, of N-vinylacetamide, of N-vinylimidazole, of 2-vinylpyridine or of 4-vinylpyridine.

Preferred cationic coagulants to be used as component (II) are acrylamide copolymers which comprise structural units which correspond to the general formula (2), and more preferably which comprise structural units which correspond to both of the general formulae (1) and (2):

wherein:

-   -   R: represents C═O, —COO(CH₂)₂— or —COO(CH₂)₃—, and     -   X⁻: represents a halide ion, preferably chloride.

These coagulants for component (II) preferably have number average molecular weights in the range from 500,000 to 50,000,000 g/mol.

Coagulants based on acrylamide copolymers to be used as component (II) are commercially available, for example, under the trade name of Praestol® (from Degussa Stockhausen, Krefeld, Germany) as flocculants for activated sludges. Preferred coagulants of the Praestol® type are Praestol® K111L, K122L, K133L, BC 270L, K 144L, K 166L, BC 55L, 185K, 187K, 190K, K222L, K232L, K233L, K234L, K255L, K332L, K 333L, K 334L, E 125, E 150 and also mixtures thereof. Praestol® 185K, 187K and 190K and also mixtures thereof are more preferred coagulating agents.

The residual levels of monomers, in particular of acrylate and/or of acrylamide monomers, in the coagulants are preferably less than 1% by weight, more preferably less than 0.5% by weight and most preferably less than 0.025% by weight (based on 100% by weight of the coagulant).

The coagulants can be used in solid form or as aqueous solutions or dispersions. It is preferred to use coagulants as aqueous dispersions or solutions.

In addition to (I) the polyurethane dispersions, and (II) the coagulants, it is also possible that these polyurethane foam forming compositions comprise (III) one or more auxiliary agents and/or additive materials.

Examples of suitable auxiliary agents and additive materials to be used as component (III) herein are foam auxiliaries such as foam formers and stabilizers, thickeners or thixotroping agents, antioxidants, light stabilizers, emulsifiers, plasticizers, pigments, fillers and/or flow control agents.

It is preferred that foam auxiliaries such as foam formers and stabilizers are included as (III) auxiliary agents and/or additive materials. Useful foam auxiliaries include, for example, commercially available compounds such as fatty acid amides, sulfosuccinamides, hydrocarbyl sulfates or sulfonates or fatty acid salts, in which case the lipophilic radical preferably contains from 12 to 24 carbon atoms, as well as alkylpolyglycosides, which are in principle known in prior art and which can be produced by reaction of long chain monoalcohols with 4 to 22 C atoms in the alkyl chain, with mono-, di- and polysaccharides, respectively (see for example Kirk-Othmer, Encyclopedia of Chemical Technology, John Wiley & Sons, Vol. 24, S. 29)

Preferred foam auxiliaries are sulfosuccinamides, alkanesulfonates or alkyl sulfates having from 12 to 22 carbon atoms in the hydrocarbyl radical, alkylbenzenesulfonates or alkylbenzene sulfates having from 14 to 24 carbon atoms in the hydrocarbyl radical, and/or fatty acid amides or fatty acid salts having from 12 to 24 carbon atoms in the hydrocarbyl radical, as well as alkylpolyglycosides.

Such fatty acid amides are preferably based on mono- or di-(C₂-C₃-alkanol)-amines. The fatty acid salts may be, for example, alkali metal salts, amine salts or unsubstituted ammonium salts.

Such fatty acid derivatives are typically based on fatty acids such as lauric acid, myristic acid, palmitic acid, oleic acid, stearic acid, ricinoleic acid, behenic acid or arachidic acid, coco fatty acid, tallow fatty acid, soya fatty acid and their hydrogenation products.

Particularly preferred foam auxiliaries are mixtures of sulfosuccinamides and ammonium stearates. These mixtures preferably comprise from 20% to 60% by weight and more preferably from 30% to 50% by weight of ammonium stearates, and preferably 80% to 40% by weight, and more preferably 70% to 50% by weight of sulfosuccinamides, in which the sum of the %'s by weight of the ammonium stearates and sulfosuccinamides totals 100% by weight of the mixture.

Commercially available thickeners can be used. Suitable thickeners include derivatives of dextrin, of starch or of cellulose such as, for example, cellulose ethers or hydroxyethylcellulose, organic wholly synthetic thickeners based on polyacrylic acids, polyvinylpyrrolidones, polymethacrylic compounds or polyurethanes (associative thickeners) and also inorganic thickeners, such as bentonites or silicas.

In principle, although not preferred, the polyurethane foam forming compositions which are essential to the present invention can also contain crosslinkers such as unblocked polyisocyanates, amide- and amine-formaldehyde resins, phenolic resins, aldehydic and ketonic resins, examples being phenol-formaldehyde resins, resols, furan resins, urea resins, carbamic ester resins, triazine resins, melamine resins, benzoguanamine resins, cyanamide resins or aniline resins.

The polyurethane foam forming compositions which are essential to the present invention typically contain, based on dry substance, (I) from 80 to 99.5 parts by weight of one or more aqueous anionically hydrophilicized dispersions, (II) from 0.5 to 5 parts by weight of one or more cationic coagulants, and optionally, (III) one or more auxiliary agents and/or additives which comprise from 0 to 10 parts by weight of one or more foam auxiliaries, from 0 to 10 parts by weight of one or more crosslinkers and from 0 to 10 parts by weight of one or more thickeners.

It is preferred that the polyurethane foam forming compositions which are essential to the present invention contain, based on dry substance, (I) from 85 to 97 parts by weight of one or more dispersions, (II) from 0.75 to 4 parts by weight of one or more cationic coagulants, and (III) one or more auxiliary agents and/or additives which comprise from 0.5 to 6 parts by weight of a foam auxiliary, from 0 to 5 parts by weight of a crosslinker, and from 0 to 5 parts by weight of thickener.

More preferably, the polyurethane foam forming compositions which are essential to the present invention contain, based on dry substance, (I) from 89 to 97 parts by weight of one or more dispersions, (II) from 0.75 to 3 parts by weight of one or more cationic coagulants, and (III) one or more auxiliary agents and/or additives which comprise from 0.5 to 5 parts by weight of a foam auxiliary, from 0 to 4 parts by weight of a crosslinker and from 0 to 4 parts by weight of thickener.

In addition to components (I) and (II), and optionally (III), other aqueous binders can also be present in the polyurethane foam forming compositions of the present invention. Such aqueous binders can be constructed, for example, of polyester, polyacrylate, polyepoxy or other polyurethane polymers. Similarly, the combination with radiation-curable binders such as described in, for example, U.S. Pat. No. 5,684,081, the disclosure of which is hereby incorporated by reference (and which is believed to correspond to EP-A-0 753 531), is also possible. It is also possible to employ other anionic or nonionic dispersions such as, for example, polyvinyl acetate, polyethylene, polystyrene, polybutadiene, polyvinyl chloride, polyacrylate and copolymer dispersions.

Frothing in the process of the present invention is accomplished by mechanical stirring of the polyurethane foam forming composition at high speeds of rotation by shaking or by decompressing a blowing gas.

Mechanical frothing can be effected using any desired mechanical stirring, mixing and/or dispersing techniques. Air is generally introduced, but nitrogen and other gases can also be used for this purpose.

The polyurethane foam thus obtained is, in the course of frothing or immediately thereafter, applied to a substrate or introduced into a mold and dried.

Application of the polyurethane foam to a substrate can be, for example, by casting or blade coating, but other conventional techniques are also possible. Multilayered application with intervening drying steps is also possible in principle.

A satisfactory drying rate for the polyurethane foams is observed at a temperature as low as 20° C., so that drying on injured human or animal tissue presents no problem. However, temperatures above 30° C. are preferably used for more rapid drying and fixing of the foams. Drying temperatures should not, however, exceed 200° C., preferably 150° C. and more preferably 130° C., since undesirable yellowing of the foams can otherwise occur, inter alia. Drying of the polyurethane foams in two or more stages is also possible.

Drying is generally effected using conventional heating and drying apparatus, such as (circulating air) drying cabinets, hot air or IR radiators. Drying by leading (or passing) the coated substrate over heated surfaces, for example rolls, is also possible.

Application and drying of the polyurethane foams can each be carried out batchwise or continuously, but the entirely continuous process is preferred.

Useful substrates on which the polyurethane foams can be applied include, for example, papers or films which facilitate simple detachment of the wound contact material before it is used to cover an injured site. Human or animal tissue such as skin can similarly serve as a substrate, so that direct closure of an injured site is possible by a wound contact material produced in situ.

The present invention further provides the polyurethane wound dressing foams which comprise the polyurethane foams obtainable by the process of the present invention.

Before drying, the foam densities of the polyurethane foams are typically in the range from 50 to 800 g/liter, preferably in the range from 100 to 500 g/liter and more preferably in the range from 100 to 250 g/liter (mass of all input materials [in g] based on the foam volume of one liter).

After drying, the polyurethane foams have a microporous, at least partial open-cell structure comprising intercommunicating cells. The density of the dried foams is typically below 0.4 g/cm³, preferably below 0.35 g/cm³, more preferably 0.01 to 0.3 g/cm³ and most preferably in the range from 0.1 to 0.3 g/cm³.

In accordance with the present invention, these dried polyurethane foams typically have a physiological saline absorbency, as measured by DIN EN 13726-1 Part 3.2, in the range of 100 to 1500%, preferably 300 to 1500% and more preferably in the range from 300 to 800% (mass of liquid taken up, based on the mass of dry foam). In addition, these dried polyurethane foams typically have a water vapor transmission rate, as measured by DIN EN 13726-2 Part 3.2, in the range from 2000 to 8000 g/24 h*m², preferably in the range from 3000 to 8000 g/24 h*m² and most preferably in the range from 3000 to 5000 g/24 h*m^(2.)

The polyurethane foams exhibit good mechanical strength and high elasticity. Typically, maximum stress of the foams is greater than 0.2 N/mm² and maximum extension of the foams is greater than 250%. Preferably, maximum stress of the foams is greater than 0.4 N/mm² and the extension is greater than 350% (determined according to DIN 53504).

After drying, the thickness of the polyurethane foams is typically in the range from 0.1 mm to 50 mm, preferably in the range from 0.5 mm to 20 mm, more preferably in the range from 1 to 10 mm and most preferably in the range from 1 to 5 mm.

The polyurethane foams can moreover be adhered, laminated or coated to or with additional materials such as, for example, materials based on hydrogels, (semi-) permeable films, coatings, hydrocolloids or other foams.

If appropriate, a sterilizing step can be included in the process of the present invention. It is similarly possible, at least in principle, for polyurethane wound dressing foams produced by the process of the present invention to be sterilized after they have been formed. Conventional sterilizing processes are used where sterilization is effected by thermal treatment chemicals such as ethylenoxide or irradiation with gamma rays for example.

It is likewise possible to add, incorporate or coat these polyurethane wound dressing foams with antimicrobially or biologically active components. Such antimicrobially or biologically active components include, for example, those which have a positive effect with regard to wound healing and the avoidance of germ loads.

Due to the wide utility of the process of the present invention and of the polyurethane wound dressing foams obtainable thereby, it is possible in principle to use this process in the industrial production of polyurethane wound dressing foams. It is similarly also possible to use this process for producing sprayed plasters, for example, in which case the polyurethane wound dressing foams are formed by direct application of the polyurethane foam forming polyurethane foam forming composition to a wound, with simultaneous frothing, and subsequent drying.

For the industrial production of polyurethane wound dressing foams, component (I) the polyurethane dispersion is optionally mixed with component (III) any of the optional foam auxiliaries of the aforementioned kind, and thereafter mechanically frothed by introduction of a gas such as air, and finally coagulated by addition of component (II) the coagulant, to obtain a further processible, coagulated foam. This foam is applied to a substrate and dried. Owing to higher productivity, drying is typically carried out at elevated temperatures in the range from 30 to 200° C., preferably in the range from 50 to 150° C. and more preferably in the range from 60 to 130° C. Preference is further given to an at least two-stage drying process, beginning at temperatures of 40 to 80° C., and with subsequent further drying at elevated temperatures of 80 to 140° C. Drying is generally carried out using conventional heating and drying apparatus such as, for example, (circulating air) drying cabinets. Application and drying can each be carried out batchwise or continuously, but preference is given to the wholly continuous process.

When the polyurethane foam forming compositions of the present inventionare used to produce a sprayed plaster, component (I) the polyurethane dispersion and component (II) the coagulant, which may each contain any optional components (III) including foam auxiliaries if necessary and/or desired, are separately provided and are then mixed with each other immediately before or during application to the tissue which is to be covered. Frothing here is accomplished by simultaneous decompression of a blowing gas which was present in at least one of the components (I) and/or (II). To consolidate the foam formed, it is subsequently dried. For drying in this embodiment, temperatures of 20 to 40° C. are sufficient. When additional heat sources such as a hair dryer or an IR red light lamp are used, forced thermal drying up to a maximum temperature of 80° C. is also possible.

-   -   (1) The blowing agents suitable for this embodiment are well         known from polyurethane chemistry. Suitable propellants are for         example n-butane, i-butane and propane and any mixtures of these         hydrocarbons. Equally suitable as propellant is also         dimethylether. Preferably, a mixture selected from n-butane,         i-butane and propane is used as propellant and the desired,         fine-porous foams can be obtained. The propellant or the mixture         of propellants is typically used in an amount from 1 to 50         wt.-%, preferably 5 to 40 wt.-%, and particularly preferred 5 to         20 wt.-%, whereas the percentage of the polyurethane dispersion         (I), coagulant (II), propellant(s) and auxiliary agents/additive         materials (III) is equal to 100 wt.-%.

Spray plasters are preferably provided in spray cans, in which (I) the polyurethane dispersion and (II) the cationic coagulant are included separately from each other, and are not mixed with each other until immediately before application. The blowing agent can be included in either or both of the components (I) and/or (II). Either or both of the components (I) and (II) may additionally, if appropriate, also contain (III) one or more auxiliary agents and/or additive materials, preferably foam auxiliaries. Casting of the polyurethane foam forming polyurethane foam forming composition is also possible, as well as spraying.

The following examples further illustrate details for the process of this invention. The invention, which is set forth in the foregoing disclosure, is not to be limited either in spirit or scope by these examples. Those skilled in the art will readily understand that known variations of the conditions of the following procedures can be used. Unless otherwise noted, all temperatures are degrees Celsius and all percentages are percentages by weight.

EXAMPLES

The solid contents were determined as specified in DIN-EN ISO 3251.

NCO contents were determined, unless explicitly stated otherwise, volumetrically as specified in DIN-EN ISO 11909.

The following substances were used in the examples: Diaminosulfonate: NH₂—CH₂CH₂—NH—CH₂CH₂—SO₃Na (45% in water) Polyol 1: Polycarbonate polyol having an OH number of 56 mg KOH/g, and a number average molecular weight of 2000 g/mol (commercially available as Desmophen ® C2200 from Bayer MaterialScience AG, Leverkusen, Germany) Polyol 2: Polytetramethylene glycol polyol having an OH number of 56 mg KOH/g, and a number average molecular weight of 2000 g/mol (commercially available as PolyTHF ® 2000 from BASF AG, Ludwigshafen, Germany) Polyol 3: Polytetramethylene glycol polyol having an OH number 112 mg KOH/g, and a number average molecular weight of 1000 g/mol (commercially available as PolyTHF ® 1000 from BASF AG, Ludwigshafen, Germany) Polyol 4: Monofunctional polyether based on ethylene oxide/propylene oxide, having a number average molecular weight of 2250 g/mol, and an OH number of 25 mg KOH/g (commercially available as LB 25 polyether from Bayer MaterialScience AG, Leverkusen, Germany) Stokal ® STA: Foam auxiliary aid based on ammonium stearate, active ingredient content: 30% (commercially available from Bozzetto GmbH, Krefeld, Germany) Stokal ® SR: Foam auxiliary aid based on succinamate, active ingredient content: about 34% (commercially available from Bozzetto GmbH, Krefeld, Germany) Simulsol ™ SL 26: alkylpolyglycoside based on dodecylalcohol, about 52% queous solution, Seppic GmbH, Cologne, DE Coagulant 1: Cationic flocculation auxiliary aid containing the structures of formulae (1) and (2), and having a solids content 25% by weight (commercially available as Praestol ® 185 K from Degussa AG, Germany)

The mean of the average particle sizes (the number average of which is reported) of the polyurethane dispersions (I) were determined using laser correlation spectroscopy. (Specifically, the instrument used was a Malvern Zetasizer 1000, Malver Inst. Limited.)

Example 1 Polyurethane Dispersion 1

987.0 g of Polyol 2, 375.4 g of Polyol 3, 761.3 g of Polyol 1 and 44.3 g of Polyol 4 were heated to 70° C. in a standard stirring apparatus. Then, a mixture of 237.0 g of hexamethylene diisocyanate and 313.2 g of isophorone diisocyanate was added at 70° C. over the course of 5 minutes, and the mixture was stirred at 120° C. until the theoretical NCO value was reached or the actual NCO value was slightly below the theoretical NCO value. The ready-produced prepolymer was dissolved with 4830 g of acetone and, during the process, cooled down to 50° C., and subsequently admixed with a solution of 25.1 g of ethylenediamine, 116.5 g of isophoronediamine, 61.7 g of diaminosulfonate and 1030 g of water metered in over 10 minutes. The mixture was subsequently stirred for 10 minutes. Then, a dispersion was formed by addition of 1250 g of water. This was followed by removal of the solvent by distillation under reduced pressure.

The white dispersion obtained had the following properties: Solids content: 61% Particle size (LKS): 312 nm Viscosity (viscometer, 23° C.): 241 mPas pH (23° C.): 6.02

Example 2 Polyurethane Dispersion 2

34.18 g of Polyol 2, 85.1 g of Polyol 3, 172.6 g of Polyol 1 and 10.0 g of Polyol 4 were heated to 70° C. in a standard stirring apparatus. Then, a mixture of 53.7 g of hexamethylene diisocyanate and 71.0 g of isophorone diisocyanate was added at 70° C. over the course of 5 minutes, and the mixture was stirred at 120° C. until the theoretical NCO value was reached or the actual NCO value was slightly below the theoretical NCO value. The ready-produced prepolymer was dissolved with 1005 g of acetone and, in the process, cooled down to 50° C. and subsequently admixed with a solution of 5.70 g of ethylenediamine, 26.4 g of isophoronediamine, 9.18 g of diaminosulfonate and 249.2 g of water metered in over 10 minutes. The mixture was subsequently stirred for 10 minutes. Then, a dispersion was formed by addition of 216 g of water. This was followed by removal of the solvent by distillation under reduced pressure.

The white dispersion obtained had the following properties: Solids content: 63% Particle size (LKS): 495 nm Viscosity (viscometer, 23° C.): 133 mPas pH (23° C.): 6.92

Example 3 Polyurethane Dispersion 3

987.0 g of Polyol 2, 375.4 g of Polyol 3, 761.3 g of Polyol 1 and 44.3 g of Polyol 4 were heated to 70° C. in a standard stirring apparatus. Then, a mixture of 237.0 g of hexamethylene diisocyanate and 313.2 g of isophorone diisocyanate was added at 70° C. over the course of 5 minutes and the mixture was stirred at 120° C. until the theoretical NCO value was reached or the actual NCO value was slightly below the theoretical NCO value. The ready-produced prepolymer was dissolved with 4830 g of acetone and, in the process, cooled down to 50° C., and subsequently admixed with a solution of 36.9 g of 1,4-diaminobutane, 116.5 g of isophoronediamine, 61.7 g of diaminosulfonate and 1076 g of water metered in over 10 minutes. The mixture was subsequently stirred for 10 minutes. Then, a dispersion was formed by addition of 1210 g of water. This was followed by removal of the solvent by distillation under reduced pressure.

The white dispersion obtained had the following properties: Solids content: 59% Particle size (LKS): 350 nm Viscosity (viscometer, 23° C.): 126 mPas pH (23° C.): 7.07

Example 4 Polyurethane Dispersion 4

201.3 g of Polyol 2, 76.6 g of Polyol 3, 155.3 g of Polyol 1, 2.50 g of 1,4-butanediol and 10.0 g of Polyol 4 were heated to 70° C. in a standard stirring apparatus. Then, a mixture of 53.7 g of hexamethylene diisocyanate and 71.0 g of isophorone diisocyanate was added at 70° C. over the course of 5 minutes and the mixture was stirred at 120° C. until the theoretical NCO value was reached or the actual NCO value was slightly below the theoretical NCO value. The ready-produced prepolymer was dissolved with 1010 g of acetone and, in the process, cooled down to 50° C. and subsequently admixed with a solution of 5.70 g of ethylenediamine, 26.4 g of isophoronediamine, 14.0 g of diaminosulfonate and 250 g of water metered in over 10 minutes. The mixture was subsequently stirred for 10 minutes. Then, a dispersion was formed by addition of 243 g of water. This was followed by removal of the solvent by distillation under reduced pressure.

The white dispersion obtained had the following properties: Solids content: 62% Particle size (LKS): 566 nm Viscosity (viscometer, 23° C.): 57 mPas pH (23° C.): 6.64

Example 5 Polyurethane Dispersion 5

201.3 g of Polyol 2, 76.6 g of Polyol 3, 155.3 g of Polyol 1, 2.50 g of trimethylolpropane and 10.0 g of Polyol 4 were heated to 70° C. in a standard stirring apparatus. Then, a mixture of 53.7 g of hexamethylene diisocyanate and 71.0 g of isophorone diisocyanate was added at 70° C. over the course of 5 minutes, and the mixture was stirred at 120° C. until the theoretical NCO value was reached or the actual NCO value was slightly below the theoretical NCO value. The ready-produced prepolymer was dissolved with 1010 g of acetone and, in the process, cooled down to 50° C. and subsequently admixed with a solution of 5.70 g of ethylenediamine, 26.4 g of isophoronediamine, 14.0 g of diaminosulfonate and 250 g of water metered in over 10 minutes. The mixture was subsequently stirred for 10 minutes. Then, a dispersion was formed by addition of 293 g of water. This was followed by removal of the solvent by distillation under reduced pressure.

The white dispersion obtained had the following properties: Solids content: 56% Particle size (LKS): 440 nm Viscosity (viscometer, 23° C.): 84 mPas pH (23° C.): 6.91

Example 6 Polyurethane Dispersion 6

1072 g of Polyol 2, 407.6 g of Polyol 3, 827 g of Polyol 1 and 48.1 g of Polyol 4 were heated to 70° C. in a standard stirring apparatus. Then, a mixture of 257.4 g of hexamethylene diisocyanate and 340 g of isophorone diisocyanate was added at 70° C. over the course of 5 minutes, and the mixture was stirred at 120° C. until the theoretical NCO value was reached or the actual NCO value was slightly below the theoretical NCO value. The ready-produced prepolymer was dissolved with 4820 g of acetone and, in the process, cooled down to 50° C. and subsequently admixed with a solution of 27.3 g of ethylenediamine, 126.5 g of isophoronediamine, 67.0 g of diaminosulfonate and 1090 g of water metered in over 10 minutes. The mixture was subsequently stirred for 10 minutes. Then, a dispersion was formed by addition of 1180 g of water. This was followed by removal of the solvent by distillation under reduced pressure.

The white dispersion obtained had the following properties: Solids content: 60% Particle size (LKS): 312 nm Viscosity (viscometer, 23° C.): 286 mPas pH (23° C.): 7.15

Examples 7-12 Foams Produced From the Polyurethane Dispersions of Examples 1-6

The polyurethane dispersions produced as described in Examples 1-6 were mixed with the foam auxiliaries as set forth in the amounts indicated in Table 1 and frothed by means of a commercially available hand stirrer (stirrer made of bent wire) to a I liter foam volume. While stirring was continued, the foams obtained were finally coagulated by addition of Coagulant 1 in the amount set forth in Table 1; coagulation left foam volume unchanged (slight increase in viscosity). Thereafter, the foams were drawn down on silicone-coated paper by means of a blade coater set to the gap height reported in Table 1. Table 1 similarly recites the drying conditions for the foams produced as indicated. Clean white foams having good mechanical properties and a fine porous structure were obtained without exception. TABLE 1 Amount (g) PU Sto- Sto- Coag- Foam Dispersion kal ® kal ® ulant SH ¹⁾ No. (Example) STA SR 1 (mm) Curing  7a 235.0 (1) 4.2 5.6 5.0 2 2 h/37° C.  7b 235.0 (1) 4.2 5.6 5.0 4 18 h/37° C.  7c 235.0 (2) 4.2 5.6 5.0 6 18 h/37° C.  7d 235.0 (2) 4.2 5.6 5.0 4 18 h/37° C., 30 min/ 120° C.  7e 235.0 (2) 4.2 5.6 5.0 6 18 h/37° C., 30 min/ 120° C. 8 235.0 (2) 4.2 5.6 5.0 4 2 h/37° C., 30 min/ 120° C. 9 235.0 (3) 4.2 5.6 5.0 4 18 h/37° C. 10  235.0 (4) 4.2 5.6 5.0 4 2 h/37° C., 30 min/ 120° C. 11  235.0 (5) 4.2 5.6 5.0 4 2 h/37° C., 30 min/ 120° C. 12   235.0 (6a) 4.2 5.6 5.0 4 2 h/37° C., 30 min/ 120° C. ¹⁾ blade coater gap height

As is evident from Table 2, all the foams exhibited a very rapid imbibition of water, a high absorbence of physiological saline (“free swell absorbency”), a very high moisture vapor transmission rate (MVTR) and also good mechanical strength, in particular after moist storage. TABLE 2 Imbibition rate ¹⁾ Free absorbency ²⁾ MVTR ³⁾ Foam No. (secs) (g/100 cm²) (g/m²*24 h)  7a Not determined 13.4 6500  7b Not determined 23.6 6300  7c Not determined 33.0 5100  7d 9 20.1 4400  7e 9 29.6 4200 8 7 21.4 4100 9 7 23.4 3700 10  18 20.2 4100 11  11 25.8 4300 12  17 22.1 4400 ¹⁾ time for complete penetration of a drop of distilled water into the foam (test on side facing the paper); ²⁾ absorption of physiological saline determined according to DIN EN 13726-1 Part 3.2 (5 test samples instead of 10 test samples); ³⁾ moisture vapor transition rate determined according to DIN EN 13726-2 Part 3.2

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Example 13

54 g of a polyurethane dispersion prepared according to example 2 were mixed with 1,37 g of Simulsol™ SL 26. This mixture was filled into one compartment of a suitable two component spray can, and 1,37 g of Praestol® 185K were filled into the other compartment of the spray can. Finally, 6 g of a mixture of propellants consisting of i-butane/n-butane/propane were added. After spraying (wet film thickness about 1 cm) and drying at ambient conditions a plain white, fine-porous foam was obtained. 

1. A process for producing polyurethane wound dressing foams comprising frothing and drying of a polyurethane foam forming composition, wherein said polyurethane foam forming composition comprises (I) at least one aqueous, anionically hydrophilicized polyurethane dispersion, and (II) at least one cationic coagulant.
 2. The process of claim 1, wherein (I) said aqueous, anionically hydrophilicized polyurethane dispersion comprises the reaction product of: A) one or more isocyanate-functional prepolymers which comprises the reaction product of: A1) at least one organic polyisocyanate, with A2) at least one polymeric polyols having a number-average molecular weight in the range from 400 to 8000 g/mol and an OH functionality in the range from 1.5 to 6, and A3) optionally, one or more hydroxyl-functional compounds having molecular weights in the range from 62 to 399 g/mol, and A4) optionally, one or more isocyanate-reactive, anionic or potentially anionic and optionally nonionic hydrophilicizing agents; with B) one or more compounds selected from the group consisting of: B1) optionally, one or more amino-functional compounds having molecular weights in the range from 32 to 400 g/mol, and B2) one or more amino-functional, anionic or potentially anionic hydrophilicizing agents; in which the free NCO groups of A) are reacted in whole or in part with chain extension, and in which the prepolymers are dispersed in water either before, during or after the reaction with component B), and with any potentially ionic groups present being converted into the ionic form by partial or complete reaction with a neutralizing agent.
 3. The process according to claim 2, wherein component A1) said organic polyisocyanate is selected from the group consisting of 1,6-hexamethylene diisocyanate, isophorone diisocyanate, the isomeric bis(4,4′-isocyanatocyclohexyl)methanes and mixtures thereof, and component A2) said polymeric polyol comprises at least 70% by weight, based on 100% by weight of A2), of a mixture comprising one or more polycarbonate polyols and one or more polytetramethylene glycol polyols.
 4. The process according to any one of claim 1, in which component (II) said cationic coagulant comprises an acrylamide copolymer which comprises structural units of the general formulae (1) and (2):

wherein in Formula (2): R: represents C═O, —COO(CH₂)₂— or —COO(CH₂)₃—; and X⁻: represents a halide ion.
 5. The process of claim 1, additionally comprising (III) one or more auxiliary agents and/or additive materials.
 6. The process of claim 5, in which (III) said auxiliary agents and/or additive materials comprise foam formers and stabilizers which are selected from the group consisting of fatty acid amides, sulfosuccinamides, hydrocarbyl sulfonates, hydrocarbyl sulfates, fatty acid salts and/or alkylpolyglycosides.
 7. The process of claim 6, in which the foam formers comprise mixtures of sulfosuccinamides and ammonium stearates, with the mixtures containing from 50 to 70% by weight of sulfosuccinamides.
 8. Polyurethane wound dressing foams produced by the process of claim
 1. 9. The polyurethane wound dressing foams of claim 8, in which the polyurethane foam is characterized by a microporous, open-cell structure and a density of less than 0.4 g/cm³ in the dried state.
 10. The polyurethane wound dressing foams of claim 8, wherein the polyurethane foams have a physiological saline absorbency of 100 to 1500% (mass of liquid taken up, based on the mass of dry foam) and a water vapor transmission rate in the range from 2000 to 8000 g/24 h*m².
 11. Polyurethane foam forming compositions comprising (I) at least one aqueous, anionically hydrophilicized polyurethane dispersion, and (II) at least one cationic coagulant. 